The present invention relates to a hydrogel product for adsorption where a non-water-soluble support matrix is cross-linked to polymers which give rise to an in water swellable adsorbent. As support matrix, an organic polymer or a combination of such, e.g. polysaccharide such as agar, cellulose, starch etc., protein and components of protein and polysaccharide.
The present invention aims for achieving an improved adsorbent which selectively binds different materials, preferably metals.
Further, the invention aims for an adsorbent which can be regenerated with required, powerful means without causing the adsorbent to be non-usable, e.g. loses its form, is e.g. eluated or treated with 20% H2SO4.
Further the invention aims for an adsorbent which effectively may bind and concentrate poisonous compounds and which is cheap enough for making an economically harmless rendering possible of such materials through e.g. dumping.
Further the invention aims for an adsorbent which makes economically recycling of small amounts of valuable metals possible, from large quantities of waste.
These aims and further advantages are obtained with the adsorbent according to the invention which in its most common embodiment is built upon a support matrix consisting of polysaccharide to which different polymers have been cross-linked with other cross-linking agents. The support matrix may also consist of protein or a mixture of protein and polysaccharide.
A polysaccharide such as agarose and cellulose may be interpreted as thread-shaped molecules consisting of monomeric units containing several hydroxyl groups and internal and external ether bonds (acetal bonds), which taken together give the polysaccharide affinity to water (it is said to be hydrophilic). Such polymers form in water swellabe gels with hydroxyls as targets for substitution.
Alkylation of the hydroxyls calls generally for a strong alkaline environment. The present invention relates to a product in which adjacent amino groups have been incorporated into the matrix. These amino groups may be alkylated under less drastic conditions (lower alkalinity than the hydroxyls).
The amino groups are part of polyalkylene imines (which actually ought to be called polyalkylene amines) which first are coupled to the polysaccharide. This can be done at a high pH e.g. 13-14. If an oligoethylene imine or polyethylene imine is selected the amino group density will be higher than the hydroxyl density in the original gel network which is an advantage for the production of the product.
U.S. Pat. No. 4,144,190, 1979 (Bowes et al.) has disclosed a polysaccharide adsorbent produced from a polysaccharide and a nitrogen containing polymer which is possible to acetylate with a cross-linking substance. Steinmann et al. (Talarta, vol 41, No 10, p 1707-1713) synthesized a similar metal adsorbent from agarose and polyethylene imine. The metal ions Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and UO22+ were studied. Our adsorbent differs from these metal adsorbents through that the carbohydrate/protein component (the support matrix) may be hydrolysed with a strong acid without causing the product to change shape macroscopically. This component may also be decomposed through oxidation with saturated sodium periodate solution. Where the gel thus retains its form despite these drastic treatments. If the product is produced in the form of particles, these may after acid treatment be packed in beds which allow high filtration velocities. These characteristics are acquired through coupling together soluble polymer with a carbohydrate-polyamine complex in a non-soluble (gel) form with a cross-linking reagent.
G. P. Royer and his group of scientists describe (J.Am.Chem.Soc. 99, 1977, p. 6141-42 (1977J.Org.Chem., 45 (1980) 2269) how an inorganic core in the form of aluminium hydroxide gel is treated with polyethylene imine followed by glutaraldehyde and reaction of the xe2x80x9cSchiffxe2x80x9d product with sodium boron hydride. The aluminium hydroxide is thereafter dissolved with hydrochloric acid. The differences between this product and the product according to the present invention are, among other things, the following:
1. We use organic polymer preferably polysaccharide and/or protein as support matrix or core material.
2. At least two, often many layers of polyethylene imine are coupled together between themselves and with the support matrix. The difference becomes particularly evident when the polymer former is a low molecular alkylene amine as e.g. tetraethylene pentamine (TEPA). Here the cross-linker may outweigh the polyethylene imine component in the end product.
3. After hydrolytic destruction (degradation) of the polysaccharide and/or the protein, an acid- and base stable residue remains from this (i.e. the support matrix) which may be manipulated chemically (e.g. be substituted). This is not the case with an inorganic core; thus no substitutable remainder is obtained with the invention according to Royer et al. This is an advantage when the polyalkylene amine product becomes hydrophilized with this remainder, most of which ought to have structure xe2x80x94Xxe2x80x94Oxe2x80x94CH2xe2x80x94CHOHxe2x80x94CH2OH and xe2x80x94Xxe2x80x94Oxe2x80x94CH2xe2x80x94CH2xe2x80x94OH where X is a cross-linking structure which has arisen during the coupling. Thus, we have after the acid treatment a stable product with both NH2, NH-groups and OH-groups of which any may be activated and substituted (with the same or different substituents). Even after acid treatment, followed by periodate treatment and final reduction with sodium boron hydride, a polyethylene imine complex remains with attached residues of polysaccharides. These residues should mainly have the structures xe2x80x94CH2xe2x80x94CHOHxe2x80x94CH2OH, and xe2x80x94CH2xe2x80x94CH2xe2x80x94OH with the cross-link to the polyethylene imine still there. These structures are to be regarded as a glycerol ether and a glycol ether, respectively and therefore it makes the product more hydrophilic and biocompatible (and thus more lenient to biological material). The glycerol and the glycol residues may be activated and thereafter substituted. As a higher pH is required for the activation of an aliphatic hydroxyl than an amine, polyamine and alcohol components may independently be activated and substituted. You may therefore substitute the polyamine with a metal chelating agent and the alcohol groups with another group, e.g. an aromatic, substance and thus obtain an adsorbent with double functions. Thus, a such adsorbent may be produced which is resistant to either a strong acid or base.
4. In the invention according to Royer et al, an inorganic core material is included and the polyethylene imine is not coupled to this through chemical combination, but the contact is through physical adsorption and through filling of canals and pores with polyethylene imine (PEI) before cross-linking. The efficiency of the capillary penetration may be questioned. According to the present invention the time for contact between the polyamine and the activated solid phase may be fiery long. All permeably available canals and pores with active groups may then react with penetrating polymer and there be fixed. Thus the contacting between reacting components is totally different.
Thus our adsorbent according to the present invention differs from these above mentioned prior art metal adsorbents through, among other things, that the carbohydrate/protein component (support matrix) may undergo drastic treatments without the product macroscopically changing shape. If then the product is produced in the form of particles, these may after treatment be packed in beds which allow high filtration velocities.
Thus, we have achieved a new adsorbent which overcomes earlier known stability problems in metal adsorbents. Furthermore we may use higher filtration velocities when Losing the present invention, which may be a great advantage in e.g. large scale processes.
The present invention relates to a hydrogel product for adsorption purposes consisting of an in water non-soluble support matrix and cross-linked polymers, characterized by that the support matrix is substituted with a first, soluble polymer material chemically bound to the support matrix, whereupon additional polymer materials are built in in the primarily synthesized support matrix polymer complex through different kinds of cross-links; optionally the support matrix may be present in the form of an acid- or base-stable residue.
Further the present invention relates to a process for production of this hydrogel product characterized by that polyalkylene imine chains A1 are incorporated into the polysaccharide/protein-network (i.e. the support matrix) which thereafter is activated and at the same time cross-linked with a cross-linking agent X1 whereupon the product is coupled to a new alkyleneimine A2 which thereupon is activated by X2, and so on, or polyalkylene imine chains A1 are incorporated into the network of the support matrix whereupon the product is reacted with a mixture of cross-linking agents and polyamine, and non-reacted reaction products are removed from the solid phase through washing.
The wording xe2x80x9csupport matrixxe2x80x9d mean in the present application a matrix which is built up of a first, in water non-soluble polymer material. The invention is demonstrated in the form of a support matrix consisting of cross-linked spherical agarose particles but the support matrix may also comprise agar particles and other polysaccharides, agarose or derivatives thereof, cellulose (e.g. cotton) or derivatives thereof, cross-linked dextran or derivatives thereof, and starch or derivatives thereof, and also proteins, or a combination of polysaccharide and protein.
The support matrix may instead of a polysaccharide comprise a protein with suitable side chains as in the case with hair (wool) and silk. They certain e.g. OH from serene and xe2x80x94Sxe2x80x94Sxe2x80x94 groups which may be converted to xe2x80x94SH and amino groups. OHxe2x80x94 groups of the serines may be converted into SH-groups. (Ebert, C., Ebert, G. and Karipp, H. xe2x80x9cOn the introduction of disulfide cross-links into fibrous proteins and bovine serum albuminxe2x80x9d, Advances in Experimental Medicine and Biologyxe2x80x9d, vol 86A, 1977, Plenum Press, New York, Editor M. Friedman, p 235-245. Thus it is possible to build up a continuous polyamine around wool or silk thread. With the above mentioned method for incorporating SHxe2x80x94 groups, the support matrix may be expanded to other protein and protein complexes. The protein is activated with a bifunctional reagent e.g. a bisepoxide, epichlorhydrin, divinyl sulphone etc whereupon the polyethylene imine is coupled and so on.
A support matrix may be built up from both protein and polysaccharide e.g. through mixing protein particles with agar in a hot solution which thereafter is allowed to congeal in a gel. Polyamine may then be built up around the gel component. In certain cases a such construction of the invention may offer certain advantages. The protein and polysaccharide may separately be enzymatically degraded, alternatively the protein may be degraded in strong alkali whereupon the polysaccharide may be degraded in acid. The intermediate may be substituted. A such selective degradation may be valuable for controlling the porosity of the end product.
The invention according to the present application may also be present in the shape of a pearl, suitably spherical, thread or membrane or may even be porous and spongy (foam plastic shaped). Thus it may be present in a rather arbitrary form.
The wording xe2x80x9can acid- and base-stable residuexe2x80x9d mean in the present application a residue which is formed when treating the support matrix with an acid, a base, an oxidizing agent or a reducing agent. The acid may be H2SO4. The treatment with oxidizing agent may be performed with saturated periodate solution at pH 7. The reducing agent may be sodium boron hydride.
The hydrogel product may also be described with the structural formula:
Pxe2x80x94Yxe2x80x94X1A1xe2x80x94X2A2xe2x80x94 . . . xe2x80x94XiAixe2x80x94XnAn
where
P is the support matrix
Y is a nitrogen-, sulphur- or oxygen bridge
X1 . . . Xi . . . Xn are same or different di, tri- or poly-functional cross-linking agents
A1 . . . Ai . . . A1 are water-soluble polymer materials, preferably same or different kinds of cross-linked residues of amines, n and i are whole numbers where i less than n and n greater than 2.
A1 . . . An may consist of, one or more, residues of a straight or branched polyalkylene amine (generally called polyalkylene imine), preferably oligo- or polyethylene amine, or residues of any of the amines NHR1R2 where R1 may be identical to or different from R2 and R may be H, alkyl, aromatic or heterocyclic alkyl, carboxyalkyl or any other amino acid.
The cross-linking agents may be of different kinds. They may be bi-, tri- or polyfunctional. The more activated functions the cross-linking agent possesses the more efficient both the cross-binding and the activation will be. A trifunctional cross-binding agent as e.g. trihalotriazine or e.g. triepoxide may be working both as cross-binding agent and activator. Cross-linking agent ,nay be halohydrin, di-, tri- or polyepoxide, halodiazine or halotriazine, di-, tri- or polyfunctional aldehyde, preferably glutaraldehyde or polymerized glutaraldehyde, di-, tri- or pulyaziridine, X1-alkylene-X2, where X1 and X2 is halogen, preferably ethylene dibromide, or halogen cyanurate.
The cross-linking agents in the products may be of different kinds whereby one or more cross-links may be broken and leave one or more other cross-links intact.
The alkylene imines which are used for production of the product according to the present application may he of a low molecular type e.g. tetraethylene pentamine or high molecular type e.g. polyethylene imine. The amine may have a linear molecular structure or it may be branched as e.g. tris(2-amino ethyl)amine, TREN. The invention relates to polyalkylene amines in general of which polyethylene amine is one example. Reliable experience gives at hand that polypropylene and pulybutylene amine give products with characteristics which do not fundamentally differ from polyethylene variants. The latter are somewhat more hydrophilic.
The invention according to the present application has a considerable stability and it places itself in a preserved, original form even after powerful chemical influence, e.g. elution, treatment using a strong acid, e.g. 20% sulphuric acid, treatment using saturated periodate solution at pH 7, or treatment using sodium boron hydride.
In order to produce the invention according to the present application, different processes may be used:
1. Polyalkylene imine chains A, are incorporated into the polysaccharide/protein-network (the support matrix) which thereafter is activated and, at the same time, cross-linked to a cross-linking agent X1 whereupon the product is coupled to a new alkyleneimine A2 which thereafter is activated X2, and so on,
2. Polyalkylene imine chains A1 are incorporated into the network of the support matrix whereupon the product is reacted with a mixture of cross-linking agents and polyamine and non-reacted reaction products are removed from the solid phase through washing. According to one embodiment of conversion products according to the present invention, the activation and the coupling are repeated several times.
3. A cross-linked polyalkylene network is first cross-linked whereupon it is coupled to the solid polysaccharide/protein-phase (support matrix), which may be cross-linked polysaccharide/protein with or without polyalkylene imine coupled according to (1) or (2).
The processes according to (1), (2) and (3) may also comprise the polysaccharide/protein-network being subjected to degradation whereby an acid- and base-stable residue is formed.
The cross-linking may be performed in another way namely through the cross-binding agent being built up on the amino units. This can be exemplified with allyl chloride or allyl bromide e.g.
Xxe2x80x94NH2+CH2xe2x95x90CHxe2x80x94CH2Brxe2x80x94 greater than Xxe2x80x94NHxe2x80x94CH2xe2x80x94CHxe2x95x90CH2xe2x80x83xe2x80x83(I)
X=the residue of the polymer
The allylamine is thereafter converted in a reactive form through halogenation e.g. bromation with bromine water:
I+Br2xe2x80x94 greater than Xxe2x80x94NHxe2x80x94CH2xe2x80x94CH2Brxe2x80x94CHBr
I+HOBrxe2x80x94 greater than Xxe2x80x94Xxe2x80x94NHxe2x80x94CH2xe2x80x94CHOHxe2x80x94CH2Br
In an alkaline solution epoxide is formed. The bromated product may be coupled to amines such as polyamines but also thiols.
This two-step activation has certain advantages. The amino groups in polyethylene imine are adjacent and ring closing comes under better control and higher capacity may be obtained. Thus you obtain a process where the activation via the polyamine units A1-An is takes place through a two-step process where first non-saturated substituents, preferably alkenyl groups, most preferred allyl groups, are incorporated at the primary and/or secondary amino groups whereupon the non-saturated substituents are desaturated with a halogen water, preferably with bromine water, whereupon the coupling to the amines thereafter preferably takes place in an alkaline environment.
The activation and the coupling may be repeated several times or first a polyalkylene network is cross-linked whereupon it is coupled to a solid polysaccharide/protein phase which may be cross-linked polysaccharide/protein with or without polyalkylene imine coupled according to what is mentioned above.
When the thus formed polyethylene imine-polyethylene imine complex in turn is cross-linked with more polyethylene imine an increasingly higher molecular polyethylene imine complex is formed which through repeatedly similar operations gives an increasingly more stable polymer complex. The thus treated particles keeps their form and may thus be subjected to extremely drastic treatment such as with a strong acid or base without losing the metal binding capability under the condition that cross-binding reagents such as epoxides, halohydrins or halogen cyanurates have been used.
It is remarkable that low molecular ethylene amines, such as e.g. tetraethylene pentamine give after repeated reactions according to what is mentioned above, very stable permeable complexes which after reaction with heavy metals such as copper ions even after strong acid treatment retain an essential amount of copper ions, obviously in a strong complex-bound form or confined in the strongly cross-linked molecular network.
In order to produce the product according to the invention there is generally required a sufficient number of, i.e. one or more, reactions involving oligo- or polyethylene imine to take place, whereby a sufficient number of layers with polyamine is obtained, preferably at least 2 layers on the support matrix, most preferred at least 3 layers.
The characteristics of the product according to the invention depends on the density of the matrix (agarose concentration in the particles) and is reflected by how molecules of different size may penetrate into the matrix.
The explanations to why the metal ions are adsorbed by the matrix may also e.g. be thanks to the great amount of amino groups in the matrix which may achieve a Z-potential which is powerful enough for the ions to be captured. The free electron pairs in the amino groups may be those who participate actively when capturing the ions. Thus it may depend upon that there is some kind of reciprocal utilization of electrons (electron delocalization). Covalent binding may be another explanation to why the invention works, as well as electrostatic forces.
Another explanation may be that ringformed (or even spherical) structures are formed which let certain metal ions through but not other. In the long run you may even specially adapt hydrogels according to the invention for special metals through using these metal ions as templates for achieving an adequate design of the gel.
These explanations above shall in any way not be limiting for the scope of the invention but serve for giving feasible explanations to how the invention in the present application works.
In the examples below the invention is demonstrated in the form of different particles e.g. Novarose(trademark) SE 10 (Novarose is a trademark owned by Inovata AB) which preferably is penetrated by protein molecules in average not much greater than 10000 Dalton, Novarose SE 100 which is penetrated by molecules approximately 10 times greater, and Novarose SE 1000 which is penetrated by molecules greater than 1 million Dalton. Some examples have also been performed with a gel which is penetrated of protein molecules with average size up to 300000 Dalton.
Application areas for the present invention may be e.g. within the area of environmental technique an order to remove non-desirable metal ions from leachate. Of course a concentration of metal ions is obtained at the same time which may be desirable to achieve in other applications such as e.g. extraction of metal. Metallurgical industry may have use of this invention partly for removal of metal ions or partly for concentration of metal ions.